Lipase-catalyzed synthesis of pungent capsaicin analogues

Pungency in peppers (Capsicum spp.) is a sensation produced by a group of molecules known as capsaicinoids. Capsaicin has been reported as the capsaicinoid with the strongest pungency. Based on the molecular structure of capsaicin the enzymatic synthesis and pungent properties of structural analogues was investigated. These analogues were based on modification of the length of the acyl chain (from C4 to C16) and the chemical substituents of the aromatic ring (–OH and –OCH3). The syntheses were carried out in 2-methyl-2-butanol with lipase B of Candida antarctica, with conversions ranging from 83% to 97.5%. The initial reaction rates were not significantly influenced by the nature of acyl-donor but rather by the substituents in the aromatic ring of the evaluated amines. The relative pungency of 10 capsaicin analogues was sensorially evaluated, using a sensory method for relative pungency. All the compounds were tested at a dose equivalent to 20 times the threshold capsaicin concentration. Two analogues were found pungent; the vanillylamides of caprylic (C-8) and capric (C-10) acids, showing a relative pungency of 66% and 36%, respectively, while the vanillylamides of caproic (C-6) and lauric (C-12) acids had a very low relative pungency (2.1% and 1.2%, respectively). From these results structural features related to pungency are discussed.